A speaker is an apparatus for reproducing a sound from an electrical signal. Reviewing a process of converting the electrical signal into the sound, the electrical signal is converted into a vibration of a diaphragm, the vibration of the diaphragm generates a wave of condensation, i.e., a sound wave to air, and the sound wave is transmitted to a human's ear through radiation.
In general, the speaker is used by coupling a low frequency reproduction speaker and a high frequency reproduction speaker. Both of the low frequency reproduction speaker and the high frequency reproduction speaker use conical speakers. A large conical speaker, which is referred to as a woofer, is used to reproduce a low frequency sound, and a small conical speaker, which is referred to as a tweeter, is used to reproduce a high frequency sound.
In order to faithfully reproduce a whole range of a sound frequency, multiple speakers are combined and used. For example, when a space is sufficient, the low frequency speaker and the high frequency speaker are separately installed, and when the space is insufficient, the high frequency speaker is disposed in the vicinity of the low frequency speaker or disposed in the low frequency speaker. In particular, since a large space cannot be used when the space is restricted like inside a vehicle, a coaxial speaker structure, in which the high frequency speaker is installed in the low frequency speaker, may be employed. That is, the small conical speaker, which is the tweeter, is installed in the large conical speaker, which is a woofer. In the coaxial speaker structure, since the tweeter is installed in the woofer, a speaker installation space can be reduced.
However, since the sound wave generated from the conical speaker is a correlation sound, a sound wave collision phenomenon, i.e., an interference phenomenon, occurs. When the interference phenomenon is generated between the sound waves generated from the woofer and the tweeter, which are conical speakers, sound resolution of the speaker system is remarkably degraded. In particular, in a vehicle in which a plurality of speakers having the coaxial speaker structure is used, this interference phenomenon is relatively severe.